In a typical cellular wireless communication system, an area is divided geographically into a number of cells and cell sectors, each defined by a radio frequency (RF) radiation pattern from a respective base station antenna. The base station antennae in the cells may then be coupled with a base station controller, which may then be coupled with a switch or gateway that provides connectivity with a transport network such as the public switched telephone network (PSTN) or the Internet.
When a mobile station, such as a cellular telephone, pager, or wirelessly-equipped computer, is positioned in a cell, the mobile station communicates via an RF air interface with the base station antennae of a cell. Consequently, a communication path can be established between the mobile station and the transport network, via the air interface, the base station, the base station controller, and the switch or gateway.
Further, in some wireless communication systems, multiple base stations are connected with a common base station controller, and multiple base stations are connected with a common switch or gateway. Each base station controller may then manage air interface resources for multiple wireless coverage areas (e.g., multiple cells and sectors), by performing functions such as assigning air interface traffic channels for use by mobile stations in the coverage areas and orchestrating handoff of calls between coverage areas. And the switch and/or gateway, in turn, may control one or more base station controllers and generally control wireless communications, by performing functions such as receiving and processing call requests, instructing base station controllers when to assign traffic channels, paging mobile stations, and managing handoff of calls between base station controllers.
In general, air interface communications in each sector (or other such coverage area) of a cellular wireless communication system can be encoded or carried in a manner that distinguishes the communications in that sector from communications in adjacent sectors. For example, in a Code Division Multiple Access (CDMA) system, each sector has a respective pseudo-random noise offset or “PN offset” that is used to encode or modulate air interface communications in the sector distinctly from those in adjacent sectors. Analogously, in other air interface protocols, communications in one sector may be distinguished from those in other sectors by frequency, time, and/or various other parameters.
Each sector may have a limited number of traffic channels that its serving base station can assign at any given time (e.g., for concurrent use by numerous mobile stations, or for other use). In CDMA, for instance, each traffic channel may be defined by encoding with a particular “Walsh code,” yet the sector may have a limited pool of such Walsh codes. Alternatively, in time division multiplex systems, such as TDMA or 1xEV-DO (e.g., the 1xEV-DO forward link for instance), traffic channels may be defined through interleaved timeslots on the air interface.
Furthermore, each sector may define an air interface “paging channel” on which the serving base station can send access probe acknowledgements and traffic channel assignment messages to served mobile stations. The paging channel may have limited capacity. (Further, if multiple access channels are provided, they may cooperatively have limited capacity.) For instance, the paging channel may define timeslots in which the base station can send various messages to particular mobile stations. If the base station has numerous such messages to send, however, the paging channel can become congested and can thereby delay call setup or the like.
When a switch in a cellular wireless communication system seeks to page a mobile station (e.g., for an incoming call or for some other reason), the switch can send the page message to numerous base stations in the switch's coverage area, with the hope that when the base stations broadcast the page message, the mobile station will receive the page message in one of the associated sectors and will respond. Given the scarcity of paging channel resources, however, most modern cellular networks are instead arranged to engage in a more targeted paging process known as “zone based paging.”
With zone based paging, a cellular network is divided into paging zones, each with a respective zone ID, and paging is performed on a zone-basis. To facilitate this, each base station in the system may broadcast as one of its overhead parameters the zone ID for the zone in which the base station is located. Mobile stations operating in the network may then programmatically monitor the zone IDs indicated in the overhead messages and may automatically register with the network when they detect that they have moved into a new zone, or for other reasons. To register with the network, a mobile station may send a registration message via the access channel in its current sector, and a switch in the network would note the mobile station's registration and convey an indication of the registration to a home location register for later reference.
With this process, the registration records thereby maintained by switches and/or home location registers will indicate the paging zone in which each mobile station last registered. When a switch seeks to page a mobile station, the switch may then efficiently send the page message to just those base stations that are within the zone of the mobile station's last registration, as it is likely that the mobile station is in that zone. Further, the switch may send the page message to the base stations in zones adjacent to the mobile station's zone of last registration, to cover the possibility that the mobile station has moved to a new zone but has not yet registered its presence in the new zone. Once the designated base stations transmit the page message, if the mobile station does not respond to the page, the switch may then broaden the scope of the page, by sending the page message to a wider range of paging zones and perhaps ultimately to all base stations in the switch's serving area.